These options control the C preprocessor, which is run on each C source file before actual compilation.
See Options Controlling the Preprocessor, for information on C preprocessor options.
Some of these options also affect how g77 processes the
INCLUDE directive.
Since this directive is processed even when preprocessing
is not requested, it is not described in this section.
See Options for Directory Search, for
information on how g77 processes the INCLUDE directive.
However, the INCLUDE directive does not apply
preprocessing to the contents of the included file itself.
Therefore, any file that contains preprocessor directives
(such as #include, #define, and #if)
must be included via the #include directive, not
via the INCLUDE directive.
Therefore, any file containing preprocessor directives,
if included, is necessarily included by a file that itself
contains preprocessor directives.